Page 35 - Ilmu Tanah

22 The Chemistry and Fertility of Soils under Tropical Weeds

2+
where X – is the soil adsorption sites and NE is nutrient element cations like Ca ,
+ 2+
K , Cu , etc. This mechanism may supply the soluble nutrient elements relatively
fast controlled by the related equilibrium constant. The process is intensified by
the lower concentration of nutrient elements caused by element absorption by
weed roots.

Weeds

H + , Acids, CO 2 Internal Sources: External

Sources:

Primary
Minerals Weathering Soluble
Nutrient
Secondary Elements
Enzymes Minerals Ads./Des/Dis Fertilizers Irrigation Deposition

Organic
Matters Decomp.

Soil Solids Soil Water

Fig. 2.1. The soil – water – nutrient element – weed relationship
(Adapted from Salam, 2014).

The second mechanism is the dissolution of secondary minerals. This may
include among which the dissolution of Mn-P stimulated by redox reaction. When
2+
the soil environment is flooded, Mn-P is reduced and dissolved to produce Mn
2+
and P ions. The presence of Mn is enhanced at low pH. Similarly, the hydroxide

Abdul Kadir Salam and Nanik Sriyani – 2019